1. Field of the Invention
This invention relates to silicon carbide (SiC) epitaxial layers grown on substrates offcut towards &lt;1100&gt;, to devices comprising Such SiC epitaxial layers, and to a method of making such SiC epitaxial layers.
2. Description of the Related Art
High doping concentrations are required to form low specific contact resistances in SiC ohmic contacts. Low ohmic contact resistances improve the performance of SiC devices. Conventional SiC homoepitaxy is performed on SiC substrates offcut towards the &lt;1120&gt; crystalline direction. N-type doping concentrations are typically in the range of 10.sup.18 atoms cm.sup.-3, with some reports describing doping levels &gt;10.sup.19 atoms.multidot.cm.sup.-, but higher doping concentrations and more efficient dopant incorporation (of both n-type and p-type dopants) are desired. Epilayers may offer lower defect densities and more controlled doping compared to substrate doping or dopant implantation into the substrate.
It is also desirable to provide a more uniform surface structure on the epitaxial layer surface. A uniform surface should facilitate the desired removal of material during device fabrication. A uniform epitaxial structure increases the ability to accurately predict how much material is removed during etching, and both the inter-wafer and the run-to-run etching variations are reduced. Smooth and uniform surfaces, especially in cases such as evaporated Schottky contact metals, will lead to improved device performance.
It is also desirable to have a more uniform surface to facilitate oxide fornation and to reduce the density of interface trap states. Further, a more uniform epitaxial surface may reduce surface disparities that can lead to undesirable electric field emitter sites and ultimately premature oxide breakdown. Improved oxide properties will lead to improved device and passivation performance.
In SiC MOSFETs, the epitaxial layer comprising the channel can be polished to remove the steps on the surface that alter channel mobility (see S. Scharnholz, E. Stein von Kamienski, A. Golz, C. Leonhard, and H. Kurz, Material Science Forum, 264-268, 1001 (1998)). The polish will be more uniform with a more uniform step structure, and MOS performance will improve. The zig-zagged step structure found on SiC offcut towards the &lt;1120&gt; is also likely to have a higher density of bonding disparities including dangling bonds that may cause high interface trap densities. Additionally, the large surface area exposed to ambient on the zig-zagged &lt;1120&gt; -offcut epitaxial surface may make this surface more reactive and prone to undesirable impurity incorporation.
It therefore is an object of the invention to provide an SiC material that minimizes or overcomes the problems of conventional SiC discussed hereinabove.
It is another object of the invention to provide a method of making SiC material of such improved character.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.